The disclosures of the following priority applications are incorporated herein by reference:
Japanese Patent Application No. 11-257872 filed Sep. 10, 1999.
Japanese Patent Application No. 11-259708 filed Sep. 14, 1999.
Japanese Patent Application No. 11-339514 filed Nov. 30, 1999.
Japanese Patent Application No. 2000-106960 filed Apr. 7, 2000.
Japanese Patent Application No. 2000-120296 filed Apr. 21, 2000.
1. Field of the Invention
The present invention relates to a vibration actuator which employs both a symmetric expansion vibration mode in the radial direction and also a vibration mode in a non-axisymmetric plane.
2. Description of the Related Art
Vibration actuators which employ both a radial symmetric expansion vibration mode and also a non-axisymmetric planar vibration mode are known. Such a vibration actuator utilizes a vibration element which simultaneously generates a radial symmetric expansion vibration mode in which it expands and contracts from the center in the direction towards the circumference (expanding and contracting in the radial direction), and also a non-axisymmetric planar vibration mode in which it is deformed in a non-axisymmetric manner within its plane. This vibration element is shaped as a circular plate having a central hole. Such vibration actuators are disclosed in Japanese Patent Publication No. 6-26994 etc., and they are well adapted to thin construction and are distinguished by high speed and high propulsive force and the like.
FIGS. 21A through 21D are figures for explanation of a prior art vibration element of a vibration actuator which employs both a radial symmetric expansion vibration mode and also a non-axisymmetric planar vibration mode.
A vibration element 10 comprises a piezoelectric element 11 and an electrode 12, etc. The piezoelectric element 11 may, for example, be formed from a piezoelectric material such as PZT or the like in the shape of a plate doughnut, and its entire surface is polarized in the thickness direction. This plate doughnut shape is formed so that its resonant frequencies in the radial symmetric expansion vibration mode (R,1) and also in the non axially symmetric planar vibration mode ((1,1)) are almost equal.
As shown in FIG. 21A, first and second fan shaped electrodes 12a and 12b are formed upon the front surface of the piezoelectric element 11. As shown in FIG. 21B, a third electrode 12c is formed over almost the entire rear surface of the piezoelectric element 11.
A first AC voltage is applied to the first electrode 12a by a drive voltage generation apparatus (not shown in the figures) which comprises an oscillator, a phase shifter, an amplifier and the like. Further, a second AC voltage which differs in electrical phase from the first AC voltage by 90xc2x0 is applied by the drive voltage generation apparatus to the second electrode 12b. The third electrode 12c upon the rear surface is connected to earth so as to be at electric ground potential.
The vibration element 10 resonates so as to vibrate in both the two above described modes by the frequency of the AC voltage which is applied being brought close to the resonant frequencies of these two modes, and thereby a radial symmetric expansion vibration and also a non-axisymmetric vibration are simultaneously generated.
As shown in FIG. 21C, the radial symmetric expansion vibration mode (R,1) is a vibration mode in which the vibration element 10 extends and withdraws in the radial direction with respect to the vibration center point A, which is at nearly the same position as the central position of the outer circumferential shape of the vibration element 10. The displacement component Ur in the radial direction is generated at the points C1 and C2 which are positioned on the circumference of the vibration element 10.
Further, as shown in FIG. 21D, the non axially symmetric planar vibration mode ((1,1)) is a vibration mode in which the vibration element 10 is repeatedly deformed leftwards and rightwards in a single plane, as shown by the dashed lines, with the points B1 and B2 being nodes, so that displacement components Uxcex8 in the directions of the arrows are generated at the points C1 and C2.
And an elliptic motion like that shown in FIG. 21A is generated as the combined displacement due to both these two vibrations in the vibration element 10 at the positions of the points C1 and C2, which are the drive force take-out portions of the vibration element 10. When the vibration element 10 is pressed into contact with a relative movement member 30 at the positions of these points C1 and C2, a frictional force is generated in the direction of displacement of the relative movement member 30, and thereby it is possible to supply direct drive force to the relative movement member 30.
Since a prior art vibration actuator takes advantage of vibration modes like those described above, it is thereby possible to realize a thin drive apparatus of small size, because according to theory the vibrational displacement only takes place in one plane.
However, when it is contemplated to apply this vibration actuator to a small sized portable electronic device which is powered by a battery, or the like, the requirement arises for the drive voltage to be reduced as much as possible. In particular, with current portable electronic devices, along with reduction of battery size, there is a tendency to reduce the voltage of the power source for the incorporated circuitry, and these requirements become more and more demanding.
A primary objective of the present invention is to provide a vibration actuator of sufficient rigidity which can drive with good efficiency relative to the drive voltage, and which moreover can drive at high torque with low drive voltage; and with which at the same time, further, the reduction of size can be anticipated with a simple and also cheap structure.
Another objective of the present invention is to provide a vibration actuator which can support its vibration element so as not to damp the vibration energy which this vibration element imparts to its relative movement member.
The vibration actuator according to the present invention includes a vibration actuator including a vibration element, which simultaneously generates a radial symmetric expansion vibration mode in which the vibration element expands and contracts in the radial direction and a non-axisymmetric planar vibration mode in which the vibration element bends to and fro in a non-axisymmetric manner within the same plane on which the radial symmetric expansion vibration is generated, and thereby drives a relative movement member. And this vibration element comprises at least one superimposed layer structure comprising an elastic member sandwiched between a pair of electrical energy to mechanical energy conversion elements.
The electrical energy to mechanical energy conversion elements and the elastic member included in this vibration actuator may be shaped as circular plates with central holes, and the elastic member is provided with a support member which supports the vibration element at at least one portion of the outer or inner circumference of the elastic member.
The electrical energy to mechanical energy conversion elements and the elastic member included in this vibration actuator may be shaped as circular plates, and the vibration actuator may further comprises a drive force take out portion, formed so as to project outwards from the outer circumference of the elastic member, and which transmits drive force obtained from vibration which is generated in the vibration element to the relative movement member.
It is desirable for the thickness of the elastic member to be equal to or greater than the thickness of the electrical energy to mechanical energy conversion elements.
Each of the pair of electrical energy to mechanical energy conversion elements may include a plurality of electrodes which are symmetrically arranged relative to the elastic member, and to each of which an AC voltage is input, with the AC voltages for the two electrical energy to mechanical energy conversion elements differing in phase. And, among this plurality of electrodes of this pair of electrical energy to mechanical energy conversion elements, those electrodes which are symmetrically arranged relative to the elastic member may be respectively supplied with AC voltages in the same phase.
The electrical energy to mechanical energy conversion elements and the elastic member comprised of the vibration element may be shaped as circular plates with central holes, and the vibration element is provided with a pressure member which presses the vibration element against the relative movement member upon the outer circumference of the vibration element or upon the inner circumference of the central hole in the vibration element.
It is desirable for the pressure member to be formed as the same member as the elastic member, and for the pressure member to support the vibration element. In this case, the pressure member may include a projecting portion which projects from the elastic member, with the vibration element being pressed against the relative movement member by the elasticity of the projecting portion.
In the vibration actuator described above, the thicknesses of the pair of electrical energy to mechanical energy conversion elements may desirably be equal. It is desirable for the thickness of the electrical energy to mechanical energy conversion elements to be equal to or less than the thickness of the elastic member. In more detail, it is desirable for the thickness of the electrical energy to mechanical energy conversion elements to be between ⅓ and {fraction (1/20)} of the overall thickness of the vibration element. Yet further, it is desirable for the structure of the vibration element including its thickness and its electrode arrangement to be upwards and downwards symmetric about the center of its thickness.
Another vibration actuator according to the present invention includes a vibration element, which simultaneously generates a radial symmetric expansion vibration mode in which the vibration element expands and contracts in the radial direction and a non-axisymmetric planar vibration mode in which the vibration element bends to and fro in a non-axisymmetric manner within the same plane on which the radial symmetric expansion vibration is generated, and thereby drives a relative movement member; and a support unit including a plurality of structual elements, which supports the vibration element. The plurality of structual elements of the support unit are arranged in superimposed layers with respect to the vibration element in the direction perpendicular to the vibration plane of the non axially symmetric planar vibration mode.
The plurality of structual elements may include: a support member which supports the vibration element; an urging member which urges the vibration element via the support member; and a guide member which guides the support member in a direction parallel to the vibration direction in the radial symmetric expansion vibration mode and only allows displacement in this predetermined direction. The support member and the urging member may be provided in a space formed by projecting the vibration surface of the vibration element to the side of the support unit. The urging member may be provided along a plane which extends in the predetermined direction of the support member. It is desirable for a plurality of the urging members to be provided, mutually opposing one another and extending along the predetermined direction of the support member.
Yet another vibration actuator according to the present invention includes: a vibration element formed as a circular plate with a central hole; a base member to which the vibration element is fixed; and a support member which supports the vibration element by the central hole thereof in order to fix the support member to the base member. One side of the support member is fixed to the base member, and the other side of the support member is fixed to the vibration element; and elastic portion is provided between a portion to which said base member is fixed and a portion to which said vibration element is fixed.
The elastic portion may be formed so that the resonance frequency xcfx89n determined by the mass of the vibration element and the rigidity of the elastic member is less than the frequency xcfx89 at which the vibration element is excited. The elastic portion of the support member may be constricted or hollow. At least the elastic portion of the support member may be made of metal. The vibration element may include an elastic member having a central hole, and a pair of electrical energy to mechanical energy conversion elements having central holes, provided upon both sides of the elastic member, and each of the pair of electrical energy to mechanical energy conversion element comprises an electrode separated into two portions along its radial direction. The support member and the elastic member may desirably be formed integrally as the same member.
Yet another vibration actuator according to the present invention includes a vibration element, which simultaneously generates a radial symmetric expansion vibration mode in which the vibration element expands and contracts in the radial direction and anon-axisymmetric planar vibration mode in which the vibration element bends to and fro in a non-axisymmetric manner within the same plane, on which the radial symmetric expansion vibration is generated, and thereby drives a relative movement member, and a base member to which the vibration element is fixed; with the vibration element including at least one superimposed layer structure including a pair of electrical energy to mechanical energy conversion elements and an elastic member sandwiched between the pair of electrical energy to mechanical energy conversion elements; and with the elastic member including a ring shaped portion to both the sides of which the pair of electrical energy to mechanical energy conversion elements are stuck, and a cylindrical shaped support portion, formed integrally with the ring shaped portion, which fixes the vibration element to the base member; and the support portion including an elastic portion which suppresses the transmission of vibration generated in the vibration element to the base member.